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Work with `Result` and optional values

Goal: produce and consume Result (success or error) and Option (a value or nothing).

Bynk has no exceptions and no null. Fallible operations return Result[T, E]; possibly-absent values are Option[T].

Construct values

commons demo {
  fn ok(n: Int) -> Result[Int, String] {
    Ok(n)
  }
  fn fail() -> Result[Int, String] {
    Err("nope")
  }
  fn wrap(n: Int) -> Option[Int] {
    Some(n)
  }
  fn empty() -> Option[Int] {
    None
  }
}

Consume with `match`

fn extract(o: Option[Int]) -> Int {
  match o {
    Some(n) => n
    None => 0
  }
}

The same form works for Result, with Ok and Err arms.

Propagate errors with `?`

Inside a function that itself returns a Result, ? unwraps an Ok or returns early on an Err:

commons demo {
  type Reps = Int where InRange(1, 100)

  fn doubled(n: Int) -> Result[Int, ValidationError] {
    let r = Reps.of(n)?
    Ok(r * 2)
  }
}

If Reps.of(n) is Err(e), doubled returns Err(e) immediately; otherwise r is the unwrapped value.